High-voltage impulse generator

ABSTRACT

A liquid dielectric capacitor comprises three metal cylinders coaxially nested within one another so that the bottoms of the outer and inner cylinders are connected to each other while the middle cylinder has its bottom facing in the opposite direction and is mounted on the outer cylinder by means of an insulator. The firing electrode of a three-electrode controlled spark gap is immersed in the liquid filling the space between the bottom of the middle cylinder and the ends of the inner cylinder, the two cylinders serving as the working electrodes of the spark gap.

United'States Patent 2 llll 3,558,908

Inventors Boris lvanovich Kulikov;

Viktor Mikhailovich Lagunov; Yury El'removich Nesterikhin; VladimirMikhailovich Fedorov, Novosibirsk, U.S.S.R.

Sept. 3, 1968 Jan. 26, 197 1 Institut Yadernoi Fiziki So AnSSSRNovofibirsk, U.S.S.R.

Appl. No Filed Patented Assignee HIGH-VOLTAGE IMPULSE GENERATOR4Chims,lDnwingFig.

u.s.c|. 307/109, 317/242 1111.- c1 ..1102m 3/06, H01f3/04 FieldofSeareh320/1;

307/lO6l09; 333/12, 73C, 96, 13; 317/242, 258, 244; 174/28; 315/39 [56]References Cited UNITED STATES PATENTS 71 1,130 10/1902 Shoemaker317/242 1,610,980 12/ 1926 Silberman 317/242 2,3 39,663 1/1944 Teare317/244X 2,41 1,140 11/1946 Lindenblad 307/ 1 06X 2,947,926 8/1960 Murch317/25 8' Primary Examiner-Terrell W. Fears Attorney-Waters, Roditi,Schwartz, & Nissen ABSTRACT: A liquid dielectric capacitor comprisesthreemetal cylinders ooa cially nested within one another so that thebottoms of the outer and inner cylinders are connected to each otherwhile the middle cylinder has its bottom facing in the oppositedirection and is mounted on the outer cylinder by means of an insulator.The firing electrode of a three-electrode controlled spark gap isimmersed in the liquid filling the space between the bottom of themiddle cylinder and the ends of the inner cylinder, the two cylindersserving as the working electrodes of the spark gap.

HIGH-VOLTAGE IMPULSE GENERATOR The present invention relates tohigh-voltage impulse generators and is intended for experimentalresearch involving the use of very strong voltage and/or current pulses,such as in thermonuclear studies for heating plasma, in laserapplications for optical pumping, etc.

There exist impulse generators which comprise a bank of paper oilcapacitors and controlled spark gaps. The paper oil dielectric has a lowspecific capacitance, because of which the internal inductance of thegenerator increases out of proportion as the rate of rise and amplitudeof the current impulse are increased. I

There also exist impulse generators using a capacitor with water as thedielectric which has a higher specific capacitance.

Such generators comprise a closed rectangular box which holds a flatplate insulated from the walls and serving as the potential plate of aplane-parallel capacitor.

Switching is accomplished by a two-electrode uncontrolled spark gapplaced in water and destroyed after each use.

, Among the disadvantages of such a design are the impossibility ofparallel operation of a great number of impulse generators, thegenerator is of a single-shot" type, and the load current cannot attaina maximum rate of rise.

An object of the present invention is to eliminate the abovedisadvantages and also to enhance the reliability of a highvoltageimpulse generator.

This and other objects are accomplished by a high-voltage impulsegenerator comprising a liquid dielectric capacitor and a spark gap inwhich, according to the invention, the liquid dielectric capacitor ismade in the form of three metal cylinderscoaxially nested within oneanother so that the bottoms of the outer and inner cylinders areconnected to each other, while the middle cylinder has its bottom turnedin the opposite direction and is mounted on the outer cylinder by meansof an insulator, while the firing electrode of a three-electrodecontrolled spark gap is immersed in the liquid filling the space betweenthe bottom of the middle cylinder and the ends of the inner cylinder,the two cylinders serving as the working electrodes of the spark gap.

The liquid dielectric may be water. For simplicity, the bottoms of theouter and inner cylinders are preferably made integral.

The type of high-voltage impulse generator disclosed herein offers thefollowing advantages.

The nesting cylindrical plates of the capacitor reduce the size andincrease the capacitance of the capacitor. The load is mechanicallyisolated from the generator and is not subject to the destructive actionof the electrohydraulic shock produced by the spark gap in water, sothat the generator can be used repeatedly. Since the spark gap is of acontrolled type, the capacitor operates as a transmission line. Becauseof this, the rate of rise of the current can be readily increased, sincethe internal impedance of the transmission line is purely resistive. Thenegligible difference in the operate time between threeelectrodecontrolled spark gaps does not interfere with parallel simultaneousoperation of a great number of impulse generators.

The invention will be better understood from the following descriptionof a preferred embodiment when read in connection with the accompanyingdrawing which shows a high-voltage impulse generator, according to theinvention.

Referring to the drawing, there is shown an impulse generator with acapacitor formed by three cylinders 1, 2 and 3, separated by water whichserves as the dielectric.

The cylinders are made of metal about lcm. thick. The dielectric may beany liquid of high insulating and dielectric properties and,consequently, of high specific capacitance.

This capacitor, acting as a transmission line, has a wave impedance of 1ohm and a capacitance of 0.1 microfarad. The cylinders l and 3 have acommon bottom. The cylinder 2 is mounted on the cylinder 1 by means ofan insulator 5. The controlled spark gap has three electrodes, theworking electrodes being the bottom 6 of the cylinder 2 and the ends 8of the cylinder 3, while the firing electrode 7 is anchored near theends 8 of the cylinder 3 by means of an insulator 9.

The energy of the hydraulic shock is absorbed by a gas-filled bellows 10the pressure inside which is atm. andwhich is attached to the bottom4 ofthe cylinder 1 inside the generator.

The impulse generator operates as follows. i

The middle cylinder 2 of the water capacitor is charged relative to theouter and inner cylinders 1 and 3 from an external source (not shown inthe drawing) to a potential of +250 kilovolts during 2 microseconds. Atthe same time, one-half of this potential is applied to the firingelectrode 7 of the spark gap. The controlled three-electrode spark gapoperates after a negative trigger pulse of 250 kilovolts is applied tothe firing electrode 7, producing an overvoltage across the spark gap.As a result, the Water capacitor produces a negative voltage pulse of250 kilovolts at 250 kiloamperes with a rise time of 50 nanoseconds,which propagates away from the spark gap between the culinders 3 and '2and then between the cylinders 1 and 2 in the direction of the load (notshown in the drawing) connected to the bottom 6.

Operating into an inductive load of about 10- henry, the impulsegenerator disclosed herein can produce impulses with an amplitude of 250kilovolts and a rise time of 50 nanoseconds, following at a frequency of4 megacycles.

In some applications it is preferable to use two impulse generatorsseries connected to a load of about l00 nanohenrys. This connectionproduces a current pulse of 250 kiloamperes with a rise time of I00 anda fall time of 5 microseconds.

We claim:

l. A high-voltage impulse generator comprising a liquid dielectriccapacitor made up of three metal cylinders nested coaxially within oneanother and constituting an outer, a mid- .dle and an inner cylinderwith the bottoms of said outer and inner cylinders connected to eachother, while the middle cylinder has its bottom facing in the oppositedirection relative to the bottoms of said outer and inner cylinders; aliquid dielectric filling the space between said cylinders; an insulatorfastening said middle cylinder to the outer cylinder; means forproducing a controlled spark gap including a firing electrode, saidinner cylinder and middle cylinder constituting working electrodes, thefiring electrode being-immersed in the liquid dielectric between theends of the inner cylinder and the bottom of the middle cylinder, andmeans at the bottom of the outer cylinder extending into the liquiddielectric between the inner and outer cylinders to absorb hydraulicshock produced in the generator.

2. A high'voltage impulse generator as claimed in claim 1 in which thedielectric is water.

3. A high-voltage impulse generator as claimed in claim] in which thebottoms of the outer and inner cylinders are integral.

4. A high-voltage impulse generator as claimed in claim 1 wherein saidmeans for absorbing hydraulic shock comprises a bellows containing apressure gas.

1. A high-voltage impulse generator comprising a liquid dielectriccapacitor made up of three metal cylinders nested coaxially within oneanother and constituting an outer, a middle and an inner cylinder withthe bottoms of said outer and inner cylinders connected to each other,while the middle cylinder has its bottom facing in the oppositedirection relative to the bottoms of said outer and inner cylinders; aliquid dielectric filling the space between said cylinders; an insulatorfastening said middle cylinder to the outer cylinder; means forproducing a controlled spark gap including a firing electrode, saidinner cylinder and middle cylinder constituting working electrodes, thefiring electrode being immersed in the liquid dieleCtric between theends of the inner cylinder and the bottom of the middle cylinder, andmeans at the bottom of the outer cylinder extending into the liquiddielectric between the inner and outer cylinders to absorb hydraulicshock produced in the generator.
 2. A high-voltage impulse generator asclaimed in claim 1 in which the dielectric is water.
 3. A high-voltageimpulse generator as claimed in claim l in which the bottoms of theouter and inner cylinders are integral.
 4. A high-voltage impulsegenerator as claimed in claim 1 wherein said means for absorbinghydraulic shock comprises a bellows containing a pressure gas.